1. Field of the Invention
This invention relates to a lift assembly, and in particular to an assembly for elevating a work platform.
2. Discussion of the Prior Art
The lift assembly described herein is designed for use on a truck or trailer. The prior art contains many examples of vehicles carrying aerial work platforms. In general, existing apparatuses include a turntable carrying a boom on which a work platform is mounted. The following are examples of patents describing arrangements of the type in question.
U.S. Pat. No. 2,954,092, which issued to Thornton-Trump on Sep. 27, 1960 discloses a mobile apparatus including a swingable boom supporting a work platform, which moves vertically and horizontally from the ground to an elevated position.
U.S. Pat. No. 2,998,861, which issued to Hotchkiss on Sep. 5, 1961 discloses an orchard crane, which is self-propelled and which carries a platform on a boom having a levelling arm for maintaining the platform in a horizontal plane. The platform is mounted on a turntable, which is rotated by cables.
U.S. Pat. No. 3,127,952, which issued to Baerg on Apr. 7, 1964 describes a mobile work platform designed to position a worker close to trees in an orchard. The platform carrying the worker is elevated and rotatable on a main support in combination with a parallelogram lift beam assembly, which maintains the platform in a substantially horizontal position during movement. The main control system of the apparatus is hydraulically actuated.
U.S. Pat. No. 4,116,304, which issued to Durnell on Sep. 26, 1978 discloses an aerial personnel lift including a bucket, the position of which is automatically controlled. In the Durnell arrangement, a telescopic boom is maintained in a vertical position using an electric motor and mercury sensor switches.
U.S. Pat. No. 4,757,875, which issued to Hade et al on Jul. 19, 1988, describes a self-propelled aerial work station including a turntable on a vehicle. A parallelogram linkage connecting the turntable to a boom supports a work platform. When the platform is being raised or while in the elevated position, the structure is within the wheel base of the vehicle to provide stability and zero tailspin.
While the prior structures described above may be generally acceptable, the apparatuses are relatively complex and consequently expensive to manufacture and maintain. The assemblies also lack positive control of the work platform, the location thereof, and maneuverability.